The present invention relates generally to a key switch, or a push button switch, and more particularly to a miniature electrical switch having an inoperative condition in which the circuit controlled by the switch is open, and an operative condition in which the push button is depressed and the circuit is closed.
The invention more particularly relates to a short travel key switch of the type comprising an electrically insulating base having a bottom and a cylindrical lateral wall defining a cavity closed by a cap, a central contact and a lateral contact both arranged on said bottom, a dome-shaped switching element received in said cavity the periphery of which is in electrical contact with the lateral contact, and which is elastically yieldable to establish an electrical connection between the two contacts in response to an axial load exerted on its convex face by the facing portion of the head of an actuator disposed in the cavity and having a stem passing through a central hole of the cap.
The invention is applicable, for example, to electronic apparatus such as motor car radio sets wherein such switches are grouped on a main printed circuit board to form a control keyboard.
Previously known switches of this type, such as the one represented in FIG. 1, have the major drawback to be insufficiently resistant to the axial load exerted on the stem of the actuator. This results in unacceptable deformation and damage of the main components of the switch. More particularly, the prior art switch cannot resist the very high axial load, on the order of 50 lbs. or greater which is applied thereon several times during certification tests such as those required by the car manufacturers.
An object of the present invention is to obviate these disadvantages by providing a switch which is highly axial load resistant.